This application claims the priority of PCT International Application No. PCT/EP99/01167, filed Feb. 23, 1999 (23.02.99) and German patent document DE 198 09 515.5, filed Mar. 5, 1998 (05.03.98), the disclosures of which is expressly incorporated by reference herein.
The invention is directed to an apparatus for intermittent conveyance and positioning of vehicles rolling on their own wheels within a production line such as used, for example, in the industrial mass production of passenger cars.
In the area of final assembly of passenger cars, it is customary after the assembly of the chassis (from which moment on the vehicles stand on their own wheels) to convey the vehicles through the subsequent assembly areas by means of apron conveyors or on runners or by means of drag chains. When vehicles are conveyed by means of slat or apron conveyors, they stand with the vehicle wheels on two slat or apron conveyors which are laid parallel to one another in the floor of the working line according to the gauge of the vehicle wheels, and are driven slowly. Individual aprons or slats can be supported on the bottom via rollers, so that the composite apron or slat structure can easily be moved forward in spite of the load exerted on individual aprons or slats by the vehicles bearing down on them.
In transport by runners, the vehicles stand with the two left-hand and the two right-hand wheels on a rail of U-shaped profile which extends over the entire vehicle length, so as to form the two runners. These runners are moved along the working line by apron conveyors laid in the floor on the right and left or in each case by means of a closely packed sequence of drivable conveying rollers. The advantage of transport by runners is that the vehicles standing on runners can be offset transversely or rotated about a vertical axis in corresponding offsetting devices. The vehicles can therefore be handled more universally, standing on runners, than when they are conveyed directly, standing on their own wheels, by slat or apron conveyors or by drag chains.
In transport by drag chains, the vehicles roll on their own wheels through the production line along rolling tracks, a drag chain or a pair of drag chains being arranged along the rolling track of one side of the vehicle approximately at the interval of a wheel width. The drag chains are provided with drivers which apply a thrust to a vehicle wheel, and convey the vehicle through the production line.
The vehicles conveyed by means of these conveying techniques do not come to a standstill in a defined position at the individual workstations. In the area where these conveying techniques are used, positional tolerances of a specific body point of xc2x110 to 20 cm in the longitudinal and/or transverse directions must be allowed for. This wide spread in position is not permissible for tasks which are to be carried out in an automated and mechanized way and which presuppose a knowledge of the exact actual position in all three positions in space.
So that an exact actual position can be determined when there is such a pronounced spread in the position of the vehicles, it would first be necessary to determine the approximate actual position of the vehicle in each case by means of a preceding measuring step; the vehicle would first, as it were, have to be xe2x80x9clocatedxe2x80x9d. Only then could this be followed by a more accurate measuring programme with complex sensor technology in order to determine the exact actual position. Moreover, since fixed or reference points, suitable for the measuring systems used in this case, on the outer skin of the vehicles vary according to the type of vehicle and are themselves even subject to some tolerances, in addition to the outlay in terms of time and investment, there would also be a problem, in detecting the actual position of the vehicles at the individual workstations accurately in each case. The productivity (which it is, of course, the precise aim to increase by the use of automation techniques) would be greatly impaired in view of the time spent in determining the exact actual position. Under some circumstances, the time gained by automation as compared with manual work, would be effectively lost by the time spent in detecting the actual position, so that automation is not worthwhile.
In the assembly areas which precede chassis assembly (and where various scopes of work are automated and mechanized) at the individual workstations the vehicle bodies are normally lifted out of the conveying slides by means of centering cones (which move into body-side reference bores) and a lifting device, and are brought very quickly into a spatial position exactly defined by means of stops. However, this technique cannot be transferred to the assembly area following the chassis assembly, since, at this later assembly stage, the vehicle floor no longer has any facilities, accessible on the underside and exactly defined spatially, for receiving the vehicles, and the previously free centering receptacles are built over and/or closed with type-specifically different components.
One object of the invention is to improve the basic generic apparatus, to the effect that vehicles of different type rolling on their own wheels can be efficiently and accurately positioned and oriented automation-compatibly and type-flexibly within a workstation of a production line in the conveying direction and transversely thereto. The term xe2x80x9caccuratelyxe2x80x9d is intended to cover a relatively small tolerance range in positioning, within which particular work operations can be carried out readily in a mechanized way or in which the vehicle can very quickly be oriented and fixed mechanically with even greater accuracy via jack attachment points or similar points on the vehicle by means of a fixed apparatus within the workstation.
This and other objects and advantages are achieved by the apparatus according to the invention, in which the vehicle is positioned longitudinally and transversely within a workstation by means of the tires. For positioning in the longitudinal direction, a pair of prismatic wheel wells is provided, in which the vehicle wheels are received exactly in position in the longitudinal direction, but floatingly in the transverse direction. Even in the case of different wheel sizes occurring in practice, this arrangement consistently achieves a longitudinal positioning of the associated vehicle axis at the same point; to be precise, centrally above the wheel wells. Transversely to the conveying direction, the vehicles can be centered exactly with the middle of the conveying line by means of the transversely floating support of the vehicle wheels and by means of a centering mechanism engaging on the tire flanks by means of centering edges and arranged so as to be countersunk in the floor of the workstation.
By the vehicles being centered in the middle, a transverse positioning which is uniform, irrespective of the track width and wheel width, is achieved. Since the centering edges bear only on the tire flank, contact with or damage to the rims is ruled out. By the vehicles being positioned according to the invention, a positional tolerance of the vehicles of approximately xc2x15 mm in the longitudinal and transverse directions can readily be achieved. So long as certain approximate filling-pressure tolerances for all the tires are maintained, this accuracy is not impaired by varying air pressure in the tires. Due to the rapid and accurate positioning of the vehicles conveyed into a new workstation, the invention facilitates the use of automation techniques in the ultimate phase of the final assembly of vehicles.
Where steerable axles are concerned, the centering edges should expediently be mounted pivotably on the associated centering mechanism, so that the centering edges can come to bear, without tilting, on the tire flanks; and, when the vehicle is being centered, no action involving force is exerted on the vehicle steering. Different type-specific center distances are taken into account by means of correspondingly long carrying rollers or floatingly mounted receiving surfaces.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.